The present application relates to gravity surveys of subterranean formations.
A gravimeter detects changes in the strength of a gravitational field measured in units of acceleration at the location of the gravimeter, which depends on the density and distance of the materials around the gravimeter. In a wellbore application, a gravimeter measures the gravity and, in some instances, the gravity gradient in the wellbore. Gravity, when referring to a measurable quantity, is used herein to refer to the strength or magnitude of the gravitational field that typically is reported in units of acceleration. The gravitational gradient is the first order spatial derivative of gravity along a specific direction in space.
Gravity and derivatives thereof depend on the composition of the surrounding subterranean formation and fluids therein. From this information, a map of a formation or a log of a wellbore may be produced that indicates where reservoir, water body, fracture, and heterogeneous portions of the formation are located. The formation maps and wellbore logs, however, tend to have low resolution due to the accuracy with which one can measure the gravity and its derivatives such as the gradient and the curvature.